The more usual manner of assembling piping systems from standard copper pipe involves the threading of the ends of the pipe, and the joining of the pipe ends to each other using internally threaded unions.
Apart from the requirement to caulk threaded unions to prevent leakage at the threads, no particular problems arise in providing a securely sealed joint.
Alternatively, the pipes are joined to each other by unions which are sweat soldered or brazed onto the respective pipe ends, this technique more commonly being employed for thin walled copper pipe.
The formation of such pipe joints in these manners is laborious and time-consuming, and in turn is a relatively expensive procedure.
Similar configurations of joints have been proposed for securing lengths of plastic pipe to each other. In this case, the joints are provided by unions which are solvent welded, heat fused or adhesively attached to the pipe ends. Again, this is a laborious and time-consuming procedure, and in turn is relatively expensive.
Further, there is the possibility that one or more of the joints provided in the system will prove defective and leaking. This, however, cannot be discovered until the entire system is completed and pressurized, at which time no opportunity exists of remaking the particular defective joints without first draining the system.
Mechanical couplings for plain ended pipes previously have been proposed, which do not require threading of the pipe ends or soldering or adhesive attachment of the connecting fittings. However, such constructions have been relegated to small diameter piping systems operating at relataively low pressures in that problems of slippage of the coupling on the pipe arise under axial loading of the pipes.
The major problem in such couplings is that some form of mechanical attachment must be provided between the coupling and the pipe in order to withstand axial loads exerted on the pipe. Provided that provision is made for absorbing axial loads on the pipe, then, such couplings can prove satisfactory in piping systems operating at considerably higher pressures and assembled from pipes of larger diameters.
Examples of mechanical connectors are to be found in U.S. Pat. Nos. 4,466,640, 4,282,175, and 4,229,025, each of which provides a coupling provided internally with gripping teeth in order to increase the holding strength of the coupling, and, to increase the pressure handling capacity of the system. However, such mechanical couplings are typically restricted because of poor pipe retention to piping systems employing pipes of 2" diameter or less.
The requirement for providing separate toothed gripping members has in turn resulted in a considerable increase in the cost of the couplings, and in the assembly of the relatively complicated couplings prior to use. Further, and in the case of the prior proposals, no opportunity exists of releasing the pipe from the coupling once it has been set. Such may be required during adjustment of the assembly or reassembly of the piping system.
A further problem is that the material from which teeth are formed must be hard enough to penetrate or "bite" the surface of the pipe so that the coupling is capable of restraining the pipe against pull-out forces produced by internal fluid pressure and external loads. Thus, a few teeth providing relatively deep penetration, or, alternatively, many teeth with little penetration are required to provide the necessary restraint. The forces required to provide this penetration are very large and difficult to achieve with suitable materials. These end restraint requirements increase with increasing pipe diameter, and prior devices have been limited to relatively small diameter pipes and tubing.